JP3625824B2 - Cellulose fiber structure with radially oriented fibers and discontinuous areas, apparatus therefor, and manufacturing method - Google Patents

Abstract

A cellulosic fibrous structure having two regions distinguished from one another by basis weight. The first region is an essentially continuous high basis weight network. The second region comprises a plurality of discrete low basis weight regions. The cellulosic fibers forming the plurality of second regions are generally radially oriented within each region. The cellulosic fibrous structure may be formed by a forming belt having zones of different flow resistances arranged in a particular ratio of flow resistances. The zones of different flow resistances provide for selectively draining a liquid carrier through the different zones of the belt in a radial flow pattern.

Description

で表されるが、ここで流動面積は、突出部59の開口部63を通る面積であるか、または以下により詳しく定義する様に、隣接する突出部59間の流動面積であり、湿潤した周囲長は液体担体と接触する区域の周囲の直線的寸法である。幾つかの一般的な形状の水圧半径は良く知られており、幾つかの一般的な形状の水圧半径を示し、不規則形状の水圧半径をどの様にして見出だすかを開示する目的で、ここに参考として含めるMark's Standard Handbook for Mechanical Engineers、第８版、の様な多くの文献に記載されている。
特定の成形機素42またはその一部の水圧半径は、単位セル、すなわち完全な突出部59およびその突出部59を取り囲む環状部分65を限定する最も小さな反復単位を考えることにより計算できる。無論、単位セルは、流れに対して最も大きな制限を与える突出部59および環状部分65の高さにおける水圧半径を測定すべきである。例えば、補強構造57からの感光性樹脂突出部59の高さは、その流動抵抗に影響することがある。突出部59にテーパ−が付いていれば、以下に表Ｉに関して説明する様に、成形機素42の空気透過性を考慮することにより、計算された水圧半径に補正を加えることができる。
その様な補正がなければ、以下に考察する、水圧半径の見掛けの比率は、成形機素42上に実際に存在する水圧半径よりも小さいであろう。下記の実施例に記載する水圧半径の率は、補正していないが、その様な実施例には十分に役立つ。
図６に関して、成形機素42に可能な単位セルを破線Ｃ−Ｃで示す。無論、単位セルから形成されるが、流路の湿潤した周囲を構成しない境界は、水圧半径の計算では考慮に入れない。
水圧半径の計算に使用する流動面積は、突出部59の真下の補強構造57により加えられる制限は考慮しない。無論、開口部63の大きさが低下するにつれて、より小さなパターンが選択されるか、あるいは開口部63の直径が小さくなるために、低坪量区域26で必要な放射状配向性を持たない、あるいは坪量により区別される３つの区域を有するセルロース性繊維構造20が形成されることがある。その様な変化は、補強構造20により課せられる流動抵抗によることがある。
図６に示す成形ベルトに関して、重要な２つの区域を下記の様に定義する。選択された区域は突出部59を取り囲む輪状周辺部を含む。特定の突出部59に対する輪状周辺部のXY方向における伸びは、突出部59から隣接する突出部59への半径方向の距離の半分である。したがって、隣接する突出部59間の区域69は、その中央に境界を有し、その境界は、隣接する突出部59の、隣接する突出部59間のその様な環状部分65を限定する輪状周辺部と接している。
その上、突出部59はＺ方向で、補強構造57の残りの部分の上のある高さまで伸びているので、突出部59の上の区域には繊維はほとんど堆積しない。というのは、補強構造57の、開口部63および隣接する突出部間の環状部分65に対応する部分に堆積する繊維は、まず突出部59の自由末端53bの高さまで蓄積しなければならず、その後で追加の繊維が開口部63中または隣接突出部59間の環状部分65中に排出されずに、突出部59の最上部に残る様になるためである。
本発明で効果的に作動することが分かっている成形ベルト42の、本発明を制限しない一例は、52二重メッシュの織り補強構造57を有する。補強構造57は、曲がり直径（warp diameter）約0.15ミリメートル（0.006インチ）、shute直径約0.18ミリメートル（0.007インチ）を有する繊維で製造され、約45〜50％の開放面積を有する。この補強構造57は、約12.7ミリメートル（0.5インチ）水の差圧で毎分約36,300標準リットル（毎分1,280標準立法フィート）の空気流を通すことができる。補強構造57の厚さは、成形ベルト42の２つの面53および55間の織りパターンにより形成される関節部を計算に入れて、約0.76ミリメートル（0.03インチ）である。
成形ベルト42の補強構造57には複数の、対称的にジグザグ配置された突出部59が接続されている。各突出部59は、隣接する突出部から約24ミリメートル（0.096インチ）の機械方向ピッチおよび約1.3ミリメートル（0.052インチ）の機械横断方向ピッチで間隔をおいて配置されている。突出部59は、１平方センチメートルあたり約47個の突出部59の密度（１平方インチあたり約200個の突出部59）で設けられている。
各突出部59は、機械横断方向の対向する角部間の幅約0.9ミリメートル（0.036インチ）および機械方向の対向する角部間の長さ約1.4ミリメートル（0.054インチ）を有する。突出部59は、Ｚ方向で、補強構造57の外側を向いた面53の基底部53aから突出部59の自由末端53bまで約0.1ミリメートル（0.004インチ）伸びている。
各突出部59は、その中心に配置され、突出部の自由末端53bから突出部59の基底部53aまで伸びる開口部63を有するので、突出部の自由末端53bが補強構造57と液体連絡している。突出部59の中心に位置する各開口部63は、一般的に長円形であり、長軸が約0.8ミリメートル（0.030インチ）で短軸が約0.5ミリメートル（0.021インチ）である。補強構造57に接続された突出部59により、成形ベルト42の空気透過性は、約12.7ミリメートル（0.5インチ）水の差圧で毎分約17,300標準リットル（毎分610標準立方フィート）である。突出部59は、補強構造57の面53aより約0.1ミリメートル上に伸びている。この成形ベルト42により、図１に示す繊維構造20が製造される。
図４に示す様に、本装置はさらに、液体担体およびその中に含まれるセルロース性繊維を成形ベルト42上に、より詳しくは成形ベルト42の不連続な直立突出部59を有する面53上に、補強構造57および突出部59が繊維性スラリーにより完全に覆われる様に堆積させるための手段44を含む。この分野で良く知られている様に、ヘッドボックス44をこの目的に使用することができる。この分野では何種類かのヘッドボックス44が公知であるが、効果的であることが分かったヘッドボックス44は、一般的に繊維性スラリーを成形ベルト42の外側を向いた面53上に連続塗布し、堆積させる、従来の２本ワイヤ式ヘッドボックス44である。
繊維性スラリーを堆積させる手段44および成形ベルト42は、一般的に一定量の液体担体および含まれるセルロース性繊維が成形ベルト42上に連続工程で堆積し得る様に、相対的に移動する。あるいは、液体担体および含まれるセルロース性繊維は成形ベルト42上にバッチ製法で堆積させることができる。成形ベルト42と堆積手段44の間の差動速度が増加する、または減少するにつれて、単位時間あたり、それぞれより大量または少量の液体担体および含まれるセルロース性繊維が成形ベルト42上に堆積し得る様に、透過性の成形ベルト42上に繊維性スラリーを堆積させる手段44を調整できるのが好ましい。
また、少なくとも約90％のコンシステンシーを有する２次元的なセルロース性繊維構造20を形成するために、繊維の未発達セルロース性繊維構造20から繊維性スラリーを乾燥させる手段50aおよび／または50bを備えることもできる。繊維性スラリーの未発達セルロース性繊維構造20の乾燥には、製紙業界で良く知られている好都合の乾燥手段50aおよび／または50bを使用できる。例えば、それぞれ単独で、または組合せて使用するプレスフェルト、熱フード、赤外放射、送風乾燥機50a、およびヤンキー乾燥ドラム50bが効果的であり、この分野で良く知られている。特に好ましい乾燥方法では、送風乾燥機50a、およびヤンキー乾燥ドラム50bを順次使用する。
所望により、本発明の装置はさらに図４に示す様なエマルションロール66を含むことができる。エマルションロール66は、上記の工程の際に、有効量の化学物質を成形ベルト42、または所望により、二次ベルト46に分配する。この化学物質は、セルロース性繊維構造20の、成形ベルト42または二次ベルト46への好ましくない付着を防止する剥離剤として作用する。さらに、エマルションロール66は、成形ベルト42または二次ベルト46に化学物質を塗布して処理し、それによってその有効寿命を延長させるのにも使用できる。好ましくは、エマルションは、成形ベルト42が繊維構造20と接触していない時に、成形ベルト42の外側を向いた幾何学的構造面53に塗布する。一般的にこれは、セルロース性繊維構造20が成形ベルト42から移動し、成形ベルト42が帰路にある時に行う。
エマルションに好適な化学物質には、水、Houston,TexasのTexaco Oil Company、からＲ＆O 68 Code 702の製品番号で販売されているRegal Oilとして知られる高速タービンオイル、Rolling Meadows,IllinoisのSherex Chemical Company,Inc.からAOGEN TA100として販売されている塩化ジメチルジステアリルアンモニウム、Cincinnati,OhioのProcter ＆ Gamble Company製のセチルアルコール、およびWayne,New JerseyのAmerican CyanamidからCyanox 1790として販売されている様な酸化防止剤を含む組成物がある。また、所望により、成形ベルト42からセルロース性繊維構造20が移動した後に残留する繊維および他の残留物を成形ベルト42から清掃するのに、クリーニングシャワーまたはスプレー（図には示していない）を使用することもできる。
本発明のセルロース性繊維構造20の製造に所望により行うが、極めて好ましい工程は、繊維構造20が乾燥した後、それを短縮することである。ここで使用する様に、「短縮」とは、繊維を再配列させ、繊維と繊維の結合を分離することにより、繊維構造20の長さを短くすることである。短縮は、幾つかの良く知られた方法で行うこともできるが、最も一般的で好ましい方法はクレープ処理である。
クレープ処理の工程は、上記のヤンキー乾燥ドラム50bを使用することにより、乾燥工程と関連させて行うことができる。クレープ処理工程では、セルロース性繊維構造20を好ましくはヤンキー乾燥ドラム50bの表面に付着させ、次いでその表面から、ドクターブレード68を使用し、ドクターブレード68と繊維構造20が付着している表面の相対的な運動により除去する。ドクターブレード68は、表面とドクターブレード68間の相対的な運動の方向に対して直交する部品で方向を決め、好ましくは実質的にそれと直交させる。
また、繊維構造20の選択された部分に差圧をかける手段を備えることもできる。差圧によりセルロース性繊維構造20の区域24および26を緻密化または脱緻密化させることができる。差圧は、液体担体が過剰に排出される前のどの工程においてセルロース性繊維構造20に作用させてもよいが、好ましくはセルロース性繊維構造20が未発達のセルロース性繊維構造20である間に作用させる。差圧をかける前に過剰の液体担体が排出されると、繊維が堅くなり過ぎ、突出部59のパターン化された列の幾何学的構造と十分に適合せず、上記の様な密度の異なった区域を有していないセルロース性繊維構造20が形成される。
所望により、セルロース性繊維構造20の区域24および26を密度によりさらに分割することができる。特に、特定の高坪量区域24または特定の低坪量区域26を緻密化または脱緻密化することができる。これは、セルロース性繊維構造20を成形ベルト42から、成形ベルト42の分離した突出部59と一致していない突出部を有する二次ベルト46に移動させることにより達成できる。移動の際、または後に、二次ベルト46の突出部がセルロース性繊維構造20の区域24および26の特定箇所を圧縮し、その様な箇所を緻密化する。無論、低坪量区域26の箇所よりも、高坪量区域24の箇所が緻密化される程度の方が大きい。
選択された箇所が二次ベルト46の突出部により圧縮されると、その様な箇所は緻密化され、繊維と繊維の結合が強くなる。その様な結合により、その様な箇所の引張強度が増加し、セルロース性繊維構造20全体の引張強度が増加する。好ましくは、過剰の液体担体が排出され、繊維が堅くなり過ぎ、突出部59のパターン化された列の幾何学的構造と十分に適合しなくなる前に緻密化を行なう。
あるいは、様々な区域24および26の選択された箇所を脱緻密化し、その様な箇所の厚さおよび吸収性を増加させることができる。脱緻密化は、セルロース性繊維構造20を成形ベルト42から、突出部59またはセルロース性繊維構造20の各区域24および26と一致しない真空透過性区域を有する二次ベルト46に移動させることにより、行なうことができる。セルロース性繊維構造20を二次ベルト46に移動させた後、正圧または大気圧より低い流体差圧を二次ベルト46の真空透過性区域にかける。この流体差圧が、真空透過性区域と一致する箇所の繊維の、二次ベルト46と直角な平面内における偏りを引き起こす。流体差圧にさらされる箇所の繊維が偏ることにより、繊維はセルロース性繊維構造20の面から離れる様に移動し、その厚さが増加する。
製法
本発明のセルロース性繊維構造20は、下記の工程を含む製法により製造することができる。第一の工程は、液体担体中に複数のセルロース性繊維を入れる。セルロース性繊維は液体担体中に溶解させるのではなく、その中に単に分散させるだけである。また、成形ベルト42の様な液体透過性で維持保持性の成形機素42を用意する。成形機素42は、液体透過性区域63および65、および直立した突出部59を有する。また、液体担体および含まれるセルロース性繊維を成形機素42上に堆積させる手段44も使用する。
成形ベルト42は、それぞれ環状部分65および開口部63により限定される高流量および低流量の液体透過性区域を有する。成形ベルト42は直立した突出部59をも有する。
液体担体および含まれるセルロース性繊維は、図６に示す成形ベルト42上に堆積させる。液体担体は２つの同時段階、つまり高流量段階および低流量段階で成形ベルト42を通って排出される。高流量段階では、液体担体は、特定の初期流量で液体透過性の高流量区域を通り、閉塞が起こる（または成形ベルト42のこの部分に液体担体が最早導入されなくなる）まで排出される。低流量段階では、液体担体は、高流量区域を通る初期流量よりも低い、特定の初期流量で成形機素42の低流量区域を通って排出される。
無論、成形ベルト42中の高および低流量区域の両方を通る流量は、両区域の予想される閉塞のために、時間と共に低下する。理論的な裏付けがあるわけではないが、高流量区域が閉塞する前に低流量区域が閉塞することがある。
理論的な裏付けがあるわけではないが、最初に起こる区域の閉塞は、流動面積、湿潤した周辺部、低流量区域の形状および分布の様なファクターに基づき、その様な区域の水圧半径が小さく、流動抵抗が大きいために、あるいはその様な区域を通る流量が大きく、繊維の堆積が大きいために起こることがある。低流量区域は、例えば、突出部59を通る開口部63を含むことができ、その開口部63は隣接する突出部59間の液体透過性環状部分65よりも大きな流動抵抗を有する。
排出の両段階において、一定のセルロース性繊維が、高および低流量区域により同時に配向上の影響を受ける。これらの影響により、繊維が放射状に配向し、無限の流動抵抗を有する突出部59の表面を横切って橋かけする。この放射状橋かけにより、それぞれの不連続低坪量区域26全体にわたって高坪量区域24が広がる。低流量区域は、低流量区域の中心で繊維を過剰に蓄積させずに、その様な橋かけが起こる様な配向上の影響を与え、中間坪量区域25が生じるのを最少に抑える、または阻止する。
開口部63と環状部分65の間の流動抵抗の比率が適切に調和することが重要である。開口部63を通る流動抵抗が小さすぎる場合、中間坪量区域25が、一般的に低坪量区域24の中心に形成されることがある。この配置により、３種類の区域を有するセルロース性繊維構造20が生じる。反対に、流動抵抗が大きすぎると、不規則な、あるいは他の非放射状の繊維分布を有する低坪量区域が生じることがある。
開口部63および環状部分65の流動抵抗は、上に記載する様に水圧半径を使用して決定することができる。以下に分析する実施例により、環状部分65の開口部63に対する水圧半径の比率は、１平方センチメートルあたり約５〜約31個の突出部59（１平方インチあたり30から200個の突出部59）を有する成形機素42に対して少なくとも約２にすべきである。より低い水圧半径、例えば少なくとも約1.1、は、１平方センチメートルあたり31個（１平方インチあたり200個）を超え、１平方センチメートルあたり約78個（１平方インチあたり500個）までの突出部59を有する成形機素42に対して好適であると考えられる。
表Ｉは、以下により詳細に分析する実施例のセルロース性繊維構造20を製造するのに使用した５種類の成形機素42の幾何学的構造を示す。表Ｉの最初の欄に関していえば、成形機素42の総表面積の百分率として示す環状部分65の面積は30％または50％である。第２の欄に示す様に、成形機素42の総表面積の百分率として示す開口部63の表面積は10〜20％である。第３の欄は、補強構造57上の突出部59の程度を示す。第４の欄には、環状部分65の開口部63に対する水圧半径の理論的比率を計算してある。第５の欄には、水圧半径の実際の比率を、以下に説明する様に計算してある。
実際の水圧半径、およびその比率は、突出部59を有する、および有していない成形機素42の空気透過性から繰り返し計算した。理論的な突出部59の大きさ、したがって水圧半径は、成形機素42の構築に使用した図面から容易に見出だせるが、製造工程に固有の変動のために、実際の大きさはある程度変化する。
突出部59、したがって環状部分65および開口部63の実際の大きさは、突出部59を有していない補強構造57の空気透過性を、突出部59を有している補強構造57の空気透過性と比較することにより、近似した。実際の空気透過性は、公知の技術を使用して容易に測定され、補強構造57を通る流動面積から突出部59を理論的に差し引いて得た値よりも小さかった。
突出部59が所定の位置にある成形機素42の、実際の、および理論的な空気透過性の差を知ることにより、突出部59の壁に環状部分65および開口部63に向かって等しくテーパ−が付いていると仮定して、その様な実際の空気流を得るのに必要な突出部59の大きさを、通常の数字を使用して、反復様式で得ることができる。

成形機素42はそれぞれ１平方センチメートルあたり31個の突出部59（１平方インチあたり200個の突出部59）を有していた。無論、単位セルの、流動面積の湿潤した周囲に対する比率だけを考慮し、その比率は単位セルの大きさが拡大しても縮小しても一定なので、水圧半径の比は突出部59および環状部分65の大きさには無関係である。
下記の表IIに示す様々な実施例のセルロース性繊維構造20の構築に使用する成形機素42には、0.52〜1.27の水圧半径を使用する。下記の表IIIに示す各実施例のセルロース性繊維構造20の構築には、水圧半径比2.05を有する成形機素42を使用する。
これらの実施例から、水圧半径比が少なくとも約２である成形機素42が効果的であると考えられる。無論、材料流量比は水圧半径比の少なくとも２乗に比例するので、レイノルズ数に応じて、少なくとも２、恐らく４を超える材料流量比が効果的であると予想される。
予想としては、本発明の成形機素42には、1.25まで低い水圧半径比を使用できる（ただし、他のファクターをその様に低い比率を補償する様に調整して）。例えば、成形機素42の絶対速度を増加する、あるいは成形機素42と液体担体の間の相対的な速度を1.0速度比の近くで調和させることができよう。また、本発明のセルロース性繊維構造20の製造に、ブラジル産ユーカリの様な短い繊維を使用するのも効果的であろう。
例えば、本発明の好適なセルロース性繊維構造20は、水圧半径比が1.50である成形機素42を使用して製造されている。成形機素42の絶対速度は約262メートル／分（800フィート／分）であり、液体担体と成形機素42の間の速度比は約1.2であった。成形機素42は、１平方センチメートルあたり31個の突出部59（１平方インチあたり200個の突出部59）を有していた。突出部59は成形機素42の総表面積の約50％を占め、その中を通る開口部63は成形機素42の表面積の約15％を占めていた。得られたセルロース性繊維構造20は、約60％の北部軟材グラフトおよび約40％の化学−熱−機械的軟材パルプ（CTMP）からなり、どちらも繊維長が約2.5〜約3.0ミリメートルであった。得られたセルロース性繊維構造20は、約25％の低坪量区域26を有し、上記の両基準内に入っていた。
実施例
表IIに示す異なったパラメータを使用し、幾つかの、本発明を限定しないセルロース性繊維構造20を製造した。試料はすべてＳ−ラップ２本ワイヤ成形機械で、ニップを通して供給し、通常通りに乾燥させる、通常の84M ４シェッド繻子織り成形ワイヤに重ね合わせた、35.6x35.6センチメートルメートル（14x14インチ）の正方形試料成形機素42を使用して製造した。これらのセルロース性繊維構造20はすべて、毎分約244メートル（毎分800フィート）の速度を有する成形機素42を使用し、液体担体を成形機素42の速度より約20％高い速度で成形機素42上に供給して製造した。得られたセルロース性繊維構造20はそれぞれ坪量が約19.5グラム／平方メートル（12ポンド/3000平方フィート）であった。
第２の欄は、表IIの実施例が、１平方センチメートルあたり５個の突出部59（１平方インチあたり30個の突出部59）または１平方センチメートルあたり31個の突出部59（１平方インチあたり200個の突出部59）の大きさの突出部59を使用して構築されたことを示している。第３の欄は、隣接する突出部59間の環状部分65における開放面積の百分率が10または20％であることを示している。第４の欄は、開口部63の断面積の大きさを突出部59の断面積の百分率として表している。第５の欄は、補強構造57上の突出部59の離れた末端53bの程度が約0.05ミリメートル（0.002インチ）〜約0.2ミリメートル（0.008インチ）であることを示している。第６の欄は、繊維の種類が、繊維長約2.5ミリメートルの北部軟材グラフトであるか、または繊維長約１ミリメートルのブラジル産ユーカリであることを示している。
得られたセルロース性繊維構造20はすべて拡大せずに、および50xおよび100xに拡大して検査した。試料は定性的に、２つの基準、すなわち１）２つの区域24および26、３つの区域24、26および一般的に低坪量区域26の中心にある中間坪量区域25の存在、および２）繊維の放射状配向性、で判定した。放射状配向性は、繊維分布の対称性および非放射状（接線方向または周方向）に配向した繊維の存在により判定した。
最後の欄は、得られたセルロース性繊維構造20の分類を示す。表IIに示す実施例の各セルロース性繊維構造20は、上記の基準を使用して次の様に主観的に分類した。

無論、どの基準を適用するかによって、一つの実施例のセルロース性繊維構造20が２つ以上の区分に入ることもある。ただ一つの基準だけが記載されている場合、他の基準は、本発明のセルロース性繊維構造20の条件に適合するものと判定した。

表IIIに関して、同じ２本ワイヤ成形機械で、フルサイズ成形ワイヤを使用し、空気乾燥により、さらに実施例のセルロース性繊維構造20を製造した。成形機素42は、それぞれ補強構造57上に約0.1ミリメートル（0.004インチ）伸びている、１平方センチメートルあたり約31個の突出部59（１平方インチあたり200個の突出部59）を有していた。突出部59は成形機素42の表面積の約50％を占め、開口部63は成形機素42の表面積の約10％を占めていた。
第２の欄に示す様に、液体担体速度の成形機素42の速度に対する比率は1.0または1.4であった。第３の欄に示す様に、液体担体は、その表面積の約０％または20％で、成形機素42を支持するロール上に衝突させた。第４の欄に示す様に、得られたセルロース性繊維構造20は、坪量が１平方メートルあたり約19.5または約25.4グラム（3,000平方フィートあたり12.0または15.6ポンド）であった。第５の欄に示す様に、表IIに関して上に記載したのと同じ繊維を使用した。第６の欄に示す様に、成形機素42は速度が230または295メートル／分（700または900フィート／分）であった。最後の欄に示す様に、得られたセルロース性繊維構造20の分類には、同じ基準を適用した。

表IIIから分かる様に、一般的に、液体担体速度の成形機素42の速度に対する比率は、これらの得られたセルロース性繊維構造20を分類するのに最も重要なファクターであった。一般的に、速度比1.0がユーカリ繊維に効果的であり、速度比1.4は一般的に北部軟材グラフト繊維に効果的であった。成形機素42の速度は、得られるセルロース性繊維構造20の分類において重要度がやや低いファクターであった。一般的に、成形機素42の速度が低下するにつれて、低坪量区域26内の不規則繊維分布の傾向も低下した。
さらに、得られるセルロース性繊維構造20は、使用する繊維の種類によって重大な影響を受けることは明らかである。一般的に、ユーカリ繊維を有するセルロース性繊維構造20は、液体担体の成形機素42に対する速度により敏感であり、低坪量区域26に放射状に配向した繊維を有する良好な２区域セルロース性繊維構造20が得られるか、あるいは好ましくない３区域セルロース性繊維構造20が得られた。北部軟材グラフト繊維を使用した場合、低坪量区域26内に境界３区域または境界不規則繊維分布を有するセルロース性繊維構造20が生じた。
変形
開口部63が貫通している突出部59を有する成形機素42の上に形成されたセルロース性繊維構造20の代わりに、図7Aおよび7Bに示す様な成形機素42上に、繊維が放射状に配向した低坪量区域26を有するセルロース性繊維構造20を製造することができる。この成形機素42では、突出部59'は放射状に分割されており、放射状に配向した部分59"の中に環状部分65"が限定される。
図7Aに示す様に、放射状部分59"を、中心で、またはその近くで接続し、中間坪量区域25の形成を防止することができる。この配置により、セルロース性繊維は、放射状部分59"の中の環状部分65"を通って流れ、放射状部分59"の中心に橋かけすることができる。
あるいは、図7Bに示す様に、放射状部分59"を中心の開口部63'で分離し、低流量区域の中心に向かって抵抗なく流れる様にすることもできる。この配置により、この変形を使用して突出部59'の放射状部分59"の中心に橋かけする必要がなく、代わりに、放射状の流れを障害なしに促進するという利点が得られる。
図7Aおよび7Bに示す実施態様では、放射状部分59"は円の扇形を含むことができる。あるいは、放射状部分59"は全体的には円形ではなく、低流量区域の中心に近付くにつれて収束させることもできる。
当業者には明らかな様に、特許請求する本発明の範囲内で多くの他の変形および組合せが可能である。その様な変形および組合せはすべて請求項の範囲内に入る。 Field of Invention
The present invention relates to a fiber structure having a plurality of areas with different basis weights. More particularly, the present invention relates to a cellulosic fiber structure having a substantially continuous high basis weight area and a discontinuous low basis weight area comprising radially oriented fibers. This cellulosic fiber structure is suitable for use in daily products.
Background of the Invention
Paper-like cellulosic fiber structures are well known in the art. Such fiber structures are commonly used today in paper towels, decorative paper, facial tissues and the like.
In order to meet consumer demand, these cellulosic fiber structures need to harmonize several antagonistic properties. For example, the cellulosic fiber structure must have sufficient tensile strength so that the cellulosic fiber structure does not tear or break during normal use or when a relatively small tear force is applied. Also, the cellulosic fiber structure must be an absorbent material that allows liquid to be rapidly absorbed and well retained by the cellulosic fiber structure. The cellulosic fiber structure also needs to be sufficiently soft so that it is comfortable to touch and does not become rough during use. The fiber structure needs to exhibit a high degree of opacity so that the user does not see it as weak or of poor quality. Against the backdrop of these antagonistic properties, cellulosic fiber structures also need to be economical so that they can be profitable by manufacturing and selling and yet be purchased by consumers.
One of the above properties, tensile strength, is the ability of the cellulosic fiber structure to retain its physical integrity during use. Tensile strength is adjusted by the weakest bond under tension in the cellulosic fiber structure. The cellulosic fiber structure does not exhibit a tensile strength greater than the tensile strength of the area of the cellulosic fiber structure that can withstand the tensile load because it is broken or torn by such weakest areas. .
The tensile strength of the cellulosic fiber structure can be improved by increasing the basis weight of the cellulosic fiber structure. However, increasing the basis weight requires the use of more cellulosic fibers during manufacture, increasing the cost for the consumer and using a larger amount of natural resources as raw material.
Absorptivity is a property of cellulosic fiber structure that can suck and hold the liquid in contact. For the desired end use for cellulosic fiber structures, both the absolute amount of liquid retained and the rate at which the fiber structure absorbs the contacted liquid must be considered. Absorbency is affected by the density of the cellulosic fiber structure. If the density of the cellulosic fiber structure is too high, the gaps between the fibers may be too small and the absorption rate may not be large enough for the intended application. If the gap is too large, the capillary attraction force of the contacted liquid is reduced and the surface tension is limited, so that the liquid is not retained by the cellulosic fiber structure.
Softness is the ability of the cellulosic fiber structure to give a particularly desirable feel to the user's skin. Softness refers to bulk modulus (fiber flexibility, fiber morphology, bond density and unsupported fiber length), surface structure (crepe frequency, size and smoothness of various areas), and adhesion- It is influenced by the sliding surface friction coefficient. Softness is inversely proportional to the ability of the cellulosic fiber structure to resist deformation in a direction perpendicular to the plane of the cellulosic fiber structure.
Opacity is the ability of a cellulosic fiber structure to block or reduce light passing through the cellulosic fiber structure. The opacity is directly related to the basis weight, density and fiber distribution uniformity of the cellulosic fiber structure. Cellulosic fiber structures having a relatively large basis weight or fiber distribution uniformity also have greater opacity for a given density. Due to the increase in density, opacity increases up to a certain point, and opacity decreases as the density is further increased beyond that point. The compromise between the various properties described above results in a cellulosic fiber structure having zero basis weight openings separated from one another in a substantially continuous network having a particular basis weight. The discontinuous openings represent areas of lower basis weight than a substantially continuous network and provide a bend perpendicular to the plane of the cellulosic fiber structure, thus the flexibility of the cellulosic fiber structure To increase. The opening has a desired basis weight and is surrounded by a continuous network structure that adjusts the tensile strength of the cellulosic fiber structure.
Cellulosic fiber structures having such openings are known from the prior art. For example, Greiner et al., U.S. Pat. No. 3,034,180 (May 15, 1962) discloses a cellulosic fiber structure having two rows of zigzag openings and a row of openings. In addition, cellulosic fiber structures having openings of various shapes have been disclosed in the prior art. For example, Greiner et al. Disclose a square opening, a diamond-shaped opening, a circular opening, and a cross-shaped opening.
However, cellulosic fiber structures having openings have several drawbacks. The opening imparts transparency to the cellulosic fiber structure and may cause the consumer to feel that the quality or strength of the structure is below a desired level. The opening is generally too large and the surface tension of the fluid to the tissue or towel product described above is generally low so that the fluid cannot be absorbed and retained sufficiently. Also, the basis weight of the network structure around the opening must be increased so that sufficient tensile strength is obtained.
In addition to having zero basis weight openings, attempts have also been made to provide cellulosic fiber structures with non-zero low basis weight areas separated from one another in a substantially continuous network. Yes. For example, US Pat. No. 4,514,345 (promulgated to Johnson et al., Apr. 30, 1985) discloses a fiber structure having a discontinuous non-zero low basis weight hexagonal section. Similar shaped patterns used in fabric structures are described in US Pat. No. 4,144,370 (promulgated on 13 March 1979 in Boulton).
The non-open cellulosic fiber structures described in these patents have the advantage of slightly increased opacity and some degree of absorbency in discontinuous low basis weight areas, but discontinuous The problem of limited burst strength of the entire cellulosic fiber structure is not solved because the tensile load is hardly supported by a non-zero low basis weight area. Also, Johnson et al. And Boulton do not disclose cellulosic fiber structures with relatively high opacity in discontinuous low basis weight areas.
Cellulosic fiber structures having multiple basis weights are generally obtained by depositing a liquid carrier in which cellulosic fibers are uniformly dispersed on a device having a forming element that holds the fibers and allows the liquid to permeate. Manufactured. The forming element is generally flat and is usually an endless belt.
U.S. Pat. No. 3,322,617, promulgated 30 March 1967, Osborne, 3,025,585, promulgated 20 March 1962, Griswold, and 3,159,530, promulgated 1 December 1964, Heller Disclose various devices suitable for the production of cellulosic fiber structures having discontinuous low basis weight areas. The discontinuous low basis weight areas according to these disclosures are formed by a pattern of upstanding protrusions connected to the forming elements of the equipment used to manufacture the cellulosic fiber structure. However, in any of the above documents, the upstanding protrusions are arranged in a regular repeating pattern. The pattern can include protrusions that are zigzag relative to adjacent protrusions or in line with adjacent protrusions. Each protrusion (either in alignment or in a zigzag arrangement) is arranged at equal intervals from adjacent protrusions. In fact, Heller et al. Use a Fourdrinier wire woven into the protrusion.
Equally spaced protrusions present another drawback in the prior art. An apparatus having this arrangement provides an even flow resistance (and therefore drainage and hence cellulosic fiber deposition) that is substantially uniform throughout the liquid permeable portion of the forming element used to produce the cellulosic fiber structure. . Since there is an equal flow resistance to the discharge of the liquid carrier in the space between adjacent protrusions, a substantially equal amount of cellulosic fibers is deposited in the liquid permeable area. Thus, the cellulosic fiber structure has a relatively homogeneous and uniform deposition, and a similar distribution and arrangement of fibers, even though the fibers are not necessarily randomly or uniformly arranged in each area of the device. Form.
A prior art disclosure in which each protrusion is not evenly spaced from adjacent protrusions is made in US Pat. No. 795,719 (promulgated on 25 July 1905, Motz). However, Motz discloses protrusions that are typically arranged in an irregular pattern, which consciously affects any one of the above characteristics, or optimizes most of the characteristics. The cellulosic fibers are not advantageously distributed as is.
Accordingly, the object of the present invention is to solve the problems of the prior art, in particular high tensile strength, without excessively sacrificing other properties or uneconomically or without excessive use of natural resources, It is to solve the problem represented by antagonistic properties that maintain high absorbency, high flexibility, and high opacity. In particular, the object of the present invention is to provide a relatively high and relatively low flow resistance for the discharge of the fiber liquid carrier in the device, to reconcile such flow resistance with each other and to be effective in low basis weight areas. It is to provide a method and apparatus for producing a cellulosic fibrous structure, such as paper, by arranging the fibers radially.
By providing areas with relatively high and relatively low resistance to flow within the apparatus, the orientation and pattern of cellulosic fiber deposition can be more effectively controlled and is not previously known in the art A cellulosic fiber structure can be obtained. In general, the flow resistance of a particular area of the molding element that is permeable to the liquid and holding the fibers and the resulting cellulosic fiber structure of the basis weight of the area corresponding to such area of the molding element There is an inverse relationship between them. Thus, of course, as the fibers are retained on the forming element, areas with relatively low flow resistance form corresponding areas with relatively high basis weight in the cellulosic fiber structure and vice versa. It is the same.
More specifically, the areas with relatively low flow resistance need to be continuous so that a continuous high basis weight fiber network structure is obtained and the tensile strength is not sacrificed. Areas with a relatively high flow resistance (form areas with relatively low basis weight in the cellulosic fiber structure and orient the fibers) are preferably discontinuous, but may also be continuous.
Furthermore, the size and spacing of the protrusions with respect to the fiber length should be considered. If the protrusions are arranged too close, cellulosic fibers may bridge between the protrusions and not deposit on the surface of the forming element.
According to the present invention, a forming element is a forming belt having a plurality of zones which are distinguished from each other by having different flow resistances. The liquid carrier is discharged through the area of the forming belt in response to the flow resistance provided by the forming belt. For example, if there are impermeable areas such as protrusions or obstructions in the molded belt, the liquid carrier will not drain through these areas and therefore there will be little or no fiber deposition in such areas. .
Thus, the flow resistance ratio between the high flow resistance zone and the low flow resistance zone is very important in determining the pattern in which the cellulosic fibers contained in the liquid carrier are deposited. In general, in a molded belt zone with a relatively low flow resistance, more liquid carrier can be discharged through such zone, so that more fibers are deposited. Of course, however, the flow resistance in a particular area on the molded belt is not constant and varies with time.
By appropriately selecting the ratio of flow resistance between the discontinuous zone with high flow resistance and the continuous zone with low flow resistance, a cellulosic fiber structure with a particularly preferred cellulosic fiber orientation can be achieved. In particular, the discontinuous areas can deposit cellulosic fibers in an essentially radial pattern and have a relatively lower basis weight than substantially continuous areas. Discontinuous areas in which cellulosic fibers are radially oriented are advantageous in terms of absorbency for specific opacity over discontinuous areas in which cellulosic fibers are randomly or non-radially oriented.
In order to solve these problems, it has a substantially continuous high basis weight area and discontinuous low and medium basis weight areas, in particular the low basis weight area is adjacent to the high basis weight area and the medium basis weight area. A cellulosic fiber structure is formed. An example of such a structure, which does not form part of the present invention, can be manufactured by co-assigned application 07 / 722,792 filed in the name of Trokhan et al. On June 28, 1991.
However, cellulosic fiber structures with discontinuous medium and low basis weight areas have certain disadvantages. In particular, the fibers in the medium basis weight area do not contribute to the ability to support the loading of the cellulosic fiber structure. Instead, these fibers are gathered together to form a monocular, which is useful for opacity but does not hang on the discontinuous low basis weight area, and thus to the distribution of the applied tensile load. Does not contribute.
Summary of the Invention
The present invention includes a single thin layer cellulosic fiber structure having at least two types of areas arranged in a non-random repeating pattern. The first area has a relatively high basis weight and includes a substantially continuous network structure (hereinafter also referred to as a network structure). The second area includes a plurality of separated areas having a relatively low basis weight and is surrounded by the first area having a high basis weight. The low basis weight area includes a plurality of substantially radially oriented fibers.
The present invention, in another aspect, includes a method of making a single thin layer cellulosic fiber structure having two types of areas arranged in a non-random repeating pattern. The method comprises the steps of providing a plurality of cellulosic fibers dispersed in a liquid carrier, a forming element holding the fibers having a liquid permeable area, and means for depositing the cellulosic fibers on the forming element. Including. Cellulosic fibers are deposited on the forming element and the liquid carrier passes through the forming element and is discharged in two simultaneous stages, a high flow stage and a low flow stage. The high and low flow stages have different initial material flows from each other so that the fibers are ejected in a substantially radially oriented pattern toward the center at the low flow stages, thereby forming the areas at the high flow stages. A plurality of discontinuous areas having a relatively lower basis weight are formed, and the fibers are radially oriented within the discontinuous low basis weight areas.
Certain fibers are affected simultaneously with respect to orientation by both flow zones. This results in radially oriented cross-linking of the impermeable portions. The low flow area has this orientation effect without excessive fiber accumulation on the area.
In yet another aspect, the present invention relates to an apparatus for forming a cellulosic fibrous structure having at least two different basis weights arranged in a non-random repeating pattern. The device is arranged in a liquid-permeable, fiber-retaining molding element having areas through which liquids containing cellulosic fibers pass and are discharged, and a non-irregular repeating pattern on the molding element , Including means for holding the cellulosic fibers in two areas having different basis weights. The two types of zones consist of a first high basis weight zone with a substantially continuous network and a plurality of discontinuous, second low basis weight zones with fibers that are substantially radially oriented.
The retaining means may include a liquid permeable reinforcement structure and a row of patterned protrusions connected thereto. The patterned row of protrusions can have liquid permeable openings therethrough and / or can be divided radially.
[Brief description of the drawings]
The invention is particularly pointed out and distinctly claimed by the claims that follow at the end of the specification, with the same parts being given the same numbers and similar parts being described with reference to the accompanying drawings. Thus, the present invention can be understood more accurately.
FIG. 1 is a top micrograph of the cellulosic fiber structure of the present invention having discontinuous regions in which the cellulosic fibers are radially oriented.
FIG.₁~ 2D_ThreeIs a top micrograph of a cellulosic fiber structure with some difference in basis weight between low and high basis weight areas. In the series of figures with each alphabet symbol, the two types of grammage are shown in the order in which each series was examined, and the increase in radial orientation is indicated by a lower case letter in the series with each alphabet symbol. The figures are shown in the order of inspection.
FIG.₁~ 3D_ThreeIs a top micrograph of a range of cellulosic fiber structures having a degree of radial orientation present in a low basis weight area. In the figures of the series with each alphabet symbol, the increase in radial orientation is shown in the order in which each series is inspected, and two types of grammage are shown in the series with each alphabet symbol. The figures are shown in the order of inspection.
FIG. 4 is a schematic side view of an apparatus that can be used to produce the cellulosic fiber structure of the present invention.
FIG. 5 is a partial side view of the molding element as seen along line 5-5 in FIG. 4 with an opening passing through each protrusion.
FIG. 6 is a partial top view of the molding machine shown in FIG.
FIGS. 7A and 7B are top views schematically illustrating another embodiment of a forming element having radially segmented protrusions that can be used to manufacture the cellulosic fiber structure of the present invention.
Detailed Description of the Invention
Product
As shown in FIG. 1, the cellulosic fibrous structure 20 of the present invention has two types of zones: a first high basis weight area 24 and a second discontinuous low basis weight area 26. Each zone 24 or 26 consists of cellulosic fibers that are close to a straight line. The cellulosic fibers in the low basis weight area 26 are arranged in an essentially radial pattern.
The fiber is a component of the cellulosic fiber structure 20, one very large dimension (along the longitudinal axis of the fiber) and two other very small dimensions (perpendicular to each other, radial and longitudinal) Both in the direction perpendicular to the axis), so it is almost linear. Observation of the fiber under a microscope reveals two other dimensions that are smaller than the major dimension of the fiber, but the other two smaller dimensions need not be substantially equal and span the entire axial length of the fiber. It need not be constant. What is important is that the fiber can bend around its axis, can be bonded to other fibers, and can be dispersed in a liquid carrier.
The fiber constituting the cellulosic fiber structure may be a synthetic product such as polyolefin or polyester, but is preferably cellulosic such as cotton linter, rayon or bagasse, more preferably softwood (gymnosperm or conifer) or Wood pulp like hardwood (angiosperms or deciduous trees). As used herein, a cellulosic fiber structure comprises at least about 50% by weight or at least about 50% by volume of cellulosic fibers, including but not limited to the above fibers, Considered “cellulosic”. Cellulose mixture of wood pulp comprising softwood fibers having a length of about 2.0 to about 4.5 millimeters and a diameter of about 25 to about 50 microns and hardwood fibers having a length of less than about 1 millimeter and a diameter of about 12 to about 25 microns Has been found to be effective for the cellulosic fiber structure 20 described herein.
When selecting wood pulp for cellulosic fiber structure 20, the fiber can be any pulp, including chemical processes such as sulfite, sulfate and soda processes, and mechanical processes such as stone-pulverized pulp. You may manufacture by a manufacturing method. Alternatively, the pulp may be produced by a combination of chemical and mechanical processes or recycled. The type, combination and treatment of fibers used is not critical to the present invention.
The cellulosic fiber structure 20 of the present invention is macroscopically two-dimensional and planar, but need not be flat. The cellulosic fiber structure 20 can have a certain degree of thickness in three dimensions. However, the third dimension is very small compared to the actual first two dimensions or to the ability to produce a cellulosic fibrous structure 20 having a relatively large dimension in the first two dimensions.
The cellulosic fiber structure 20 of the present invention consists of a single thin layer. Of course, however, one or both of the two or more single thin layers produced according to the present invention can be connected in a face-to-face relationship to form a thin layer that cannot be divided. The cellulosic fiber structure 20 of the present invention is removed as a single sheet from the forming element described below and before drying, the thickness remains unchanged unless fibers are added to or removed from the sheet. Is considered a “single thin layer”. Cellulosic fiber structure 20 may or may not be embossed in a later step as desired.
The cellulosic fibrous structure 20 of the present invention is bounded by intensive properties that distinguish each region from each other. For example, the basis weight of the fiber structure 20 is one intensive property that distinguishes each area from each other. As used herein, a property is considered “intensive” if it does not have a value that depends on the set of values in the plane of the cellulosic fiber structure 20. Examples of intensive properties include cellulosic fiber structure 20 density, protruding capillary size, basis weight, temperature, compression and tensile modulus, fiber orientation, and the like. As used herein, a property that depends on a collection of various values of the subordinate tissue or components of the cellulosic fibrous structure 20 is considered “global”. Examples of regional characteristics include the weight, mass, volume, and mole of cellulosic fibrous structure 20. The most important intensive property for the cellulosic fiber structure described and claimed herein is basis weight.
The cellulosic fibrous structure 20 of the present invention has at least two different basis weights that are divided between at least two distinguishable areas called “zones” of the cellulosic fibrous structure 20. As used herein, “basis weight” is the weight of cellulosic fiber structure 20 measured by gravity, in unit area viewed in the plane of cellulosic fiber structure 20. The size and shape of the unit area for measuring basis weight depends on the relative and absolute size and shape of the areas 24 and 26 having different basis weights.
As will be apparent to those skilled in the art, within a given area 24 or 26, if such a particular area 24 or 26 is considered to have one basis weight, the normal expected basis weight variation And changes may occur. For example, when measuring the basis weight of the gap between fibers on a microscopic level, the apparent basis weight will be zero, but in practice such areas 24 or 26 unless the openings of cellulosic fiber structure 20 are measured. The basis weight of is greater than zero. Such variations and changes are normal and are the expected results of the manufacturing process.
There is no need for exact boundaries to divide adjacent areas 24 or 26 having different basis weights or to define sharp boundaries between adjacent areas 24 or 26 having different basis weights. It is only important that the distribution of fibers per unit area is different at different locations of the cellulosic fiber structure 20, and that such different distributions occur in a non-random repeating pattern. Such a non-random repeating pattern corresponds to a non-random repeating pattern in the geometry of the liquid-permeable, fiber-retaining molding element used to make the cellulosic fiber structure 20.
From an opacity standpoint, it is desirable to have a uniform basis weight throughout the cellulosic fiber structure 20, but a cellulosic fiber structure 20 having a uniform basis weight has other characteristics of cellulosic fiber structure 20. Not optimal. Due to the different basis weights of the different areas 24 and 26 of the cellulosic fibrous structure 20 of the present invention, the properties within each area 24 and 26 are different.
For example, the high basis weight area 24 provides the ability to support tensile loads, a preferred absorption rate, and imparts opacity to the cellulosic fibrous structure 20. The low basis weight area 26 stores the absorbed liquid and saves fiber when the high basis weight area 24 is saturated.
Preferably, the non-random repeating pattern is grid-like so that adjacent areas 24 and 26 cooperate and are advantageously juxtaposed. By “not irregular”, the intensively defined areas 24 and 26 are considered predictable and can be obtained by known, predetermined features of the equipment used in the manufacturing process. The term “repeating” as used herein means that the pattern is formed more than once in the fiber structure 20.
Of course, if the fiber structure 20 is very large in the manufactured state and the areas 24 and 26 are very small compared to the size of the fiber structure 20 being manufactured, i.e. changes in several orders of magnitude, the areas Although it is very difficult or impossible to absolutely predict the exact distribution and pattern between 24 and 26, the pattern is still considered irregular. However, it is only important that such intensively defined areas 24 and 26 are dispersed in a desired pattern to give the cellulosic fibrous structure 20 suitable properties for its intended purpose.
Intensively differentiated areas 24 and 26 of cellulosic fibrous structure 20 may be “discontinuous” such that adjacent areas 24 or 26 having the same basis weight are not continuous. Alternatively, areas 24 or 26 may be continuous.
It will be apparent to those skilled in the art that there may be a small transition area having a basis weight intermediate that of the adjacent area 24 or 26, but the transition area itself is what is the basis weight of the adjacent area 24 or 26. Not as important as it can be considered to constitute different basis weights. Such transition zones are within the inherent normal manufacturing tolerances known in the manufacture of the fiber structure 20 of the present invention.
The pattern size of the fiber structure 20 is about 3 to about 78 discontinuous areas 26 per square centimeter (20 to 500 discontinuous areas per square inch), preferably about 16 to about 47 discontinuities per square centimeter. Area 26 (100-300 discontinuous areas per square inch) can be included.
As will be apparent to those skilled in the art, as the pattern becomes finer (contains more discontinuous areas 24 or 26 per square centimeter), a relatively large amount of small sized hardwood fiber is used, Accordingly, the amount of larger size softwood fibers can be reduced. If too many large size fibers are used, such fibers will not conform to the geometry of the apparatus for producing the fiber structure 20 described below. If the fibers do not fit, such fibers will bridge the various geometric areas of the device, resulting in an unpatterned fiber structure 20. Cellulosic fiber structure 20 comprising about 100% hardwood fibers, especially Brazilian eucalyptus, having about 31 discontinuous areas 26 per square centimeter (200 discontinuous areas 26 per square inch) 20 It was found to be effective.
When the cellulosic fiber structure 20 shown in FIG. 1 is used as a daily product such as a paper towel or tissue, the high basis weight area 24 of the cellulosic fiber structure 20 is divided into two in the plane of the cellulosic fiber structure 20. It is preferably substantially continuous in the orthogonal direction. Such orthogonal directions need not be parallel and perpendicular to the edge of the final product, or parallel and perpendicular to the direction of manufacture of the product, but the tensile strength is cellulosic in two orthogonal directions. It is important that the structure is able to withstand the applied tensile load without being easily broken by the tensile load given to the structure. Preferably, the continuous direction is parallel to the direction of tensile load expected for the final product of the invention.
The high basis weight area 24 is substantially continuous and extends essentially throughout the cellulosic fibrous structure 20 for the embodiments described herein. Conversely, the low basis weight areas 26 are discontinuous, isolated from each other and separated by a high basis weight area 24.
An example of a substantially continuous network is the high basis weight area 24 of the cellulosic fibrous structure 20 of FIG. Other examples of cellulosic fiber structures having a substantially continuous network structure are incorporated herein by reference for the purpose of illustrating another cellulosic fiber structure having a substantially continuous network structure. U.S. Pat. No. 4,637,859 (proposed in Trokhan on Jan. 20, 1987). Interruptions in a substantially continuous network structure are not preferred, but are acceptable as long as such interruptions do not significantly adversely affect the material properties of such portions of cellulosic fibrous structure 20.
Conversely, the low basis weight areas 26 may be discontinuous and distributed throughout the high basis weight substantially continuous network 24. The low basis weight area 26 is considered to be like an island surrounded by a high continuous area 24 having a substantially continuous network structure. The discontinuous low basis weight areas 26 also form a non-random repeating pattern.
The discontinuous low basis weight areas 26 may be arranged zigzag or aligned in either or both of the two orthogonal directions described above. Preferably, a small transition area may be included as described above, but a high basis weight substantially continuous network 24 is a patterned network that surrounds a discontinuous low basis weight area 26. Form.
A basis weight difference (within the same cellulosic fibrous structure 20) between the high and low basis weight areas 24 and 26 is considered important to the present invention. If it is desirable to quantitatively measure the basis weight in each of the areas 24 and 26, and therefore if it is desired to quantitatively measure the difference in basis weight between such areas 24 and 26, then the areas 24 and 24 of the cellulosic fibrous structure 20 U.S. Patent Application No. 07, filed June 28, 1991, in the name of Phan et al., Incorporated herein by reference for the purpose of illustrating a preferred method for quantitatively measuring a basis weight of 26. A quantitative method such as soft X-ray image analysis described in Japanese Patent No. 724,551 can be used.
The area of a particular low or medium basis weight area 26 or 25 can be measured quantitatively by overlaying a photo of such area 26 or 25 with a transparent sheet having a constant thickness and a constant density. it can. Trace the border of area 26 or 25 with a color that contrasts with the border of the photo. The contour is cut as accurately as possible along this trace and then weighed. This weight is compared to the weight of a similar sheet having a unit area or other known area. The weight ratio of these sheets is directly proportional to the ratio of the two areas.
If one wants to know the relative surface area of the two areas, such as the surface area percentage of the intermediate basis area 25 within the low basis area 26, the sheet in the low basis area 26 may be weighed. A trace at the boundary of the intermediate basis weight area 25 is then cut from the sheet and the sheet is weighed. These weight ratios give the area ratio.
The difference in basis weight of the two areas 24 or 26 can be measured qualitatively and semi-quantitatively by the increasing difference scale shown by the series 2A to series 2D figures, respectively.
FIG.₁~ 2A_ThreeFigure 2A₁Have openings as shown in Figure 2A₂~ 2A_ThreeAs shown, a low basis weight area 26 having a very pronounced intermediate basis weight area 25 formed therein is shown. FIG.₁~ 2A_ThreeIn order, it can be seen that the radial orientation is increased.
FIG.₁Shows that the cellulosic fibrous structure 20 still has an intermediate basis weight area 25, which is shown in FIG.₂~ 2A_ThreeIs not more noticeable than that.
FIG.₁Indicates that only an intermediate basis weight area 25 in the initial stage of formation exists.
2D₁~ 2D_ThreeShows a cellulosic fiber structure 20 without an intermediate basis weight area 25. Fiber 2D₁From a very randomly oriented fiber, as shown in Figure 2D_ThreeAs shown, there is even a highly radially oriented fiber, and there is no significant non-uniformity in the intermediate basis weight area 25, opening, or basis weight within the low basis weight area 26.
The fibers of the two zones 24 and 26 are advantageously oriented in different directions. For example, the fibers that comprise a substantially continuous high basis weight area 24 are generally formed of a substantially continuous network structure and manufacturing process of an annular portion 65 between adjacent protrusions 59, as shown in FIG. The orientation is preferably in a single direction corresponding to the influence of the machine direction.
With this alignment, the fibers are generally parallel to each other, giving the fibers a relatively high degree of bonding. A relatively high degree of bonding results in a relatively high tensile strength in the high basis weight area 24. Such high tensile strength is generally advantageous for the relatively high basis weight areas 24 because the high basis weight areas 24 support and transmit the applied tensile load throughout the cellulosic fibrous structure 20.
The low basis weight areas 26 include fibers that are oriented radially and extend outwardly from the center of each low basis weight area 26. For the purposes of the present invention, whether or not a fiber is considered "essentially radially oriented" is determined by a measure of increasing radial orientation, shown in series 3A to series 3D, respectively. The
FIG.₁~ 3A_ThreeShows a cellulosic fiber structure 20 having a low basis weight area 26 that is free of a plurality of essentially radially oriented fibers. In particular, FIG.₁Shows a cellulosic fiber structure 20 with only one strand of radially oriented fibers and thus poor radial symmetry. FIG.₂~ 3A_ThreeShows a low basis weight area 26 in which the fibers are generally randomly distributed. FIG.₁~ 3A_ThreeAre examined in turn, an increasing trend towards cellulosic fiber structures 20 having two basis weights can be observed.
FIG.₁Shows a cellulosic fiber structure 20 with somewhat higher radial fiber distribution but still very poor radial symmetry of these fibers.
FIG.₁~ 3C₂Shows a cellulosic fiber structure 20 with low basis weight areas 26 oriented essentially radially in the low basis weight areas 26. The radially oriented fibers are distributed fairly evenly across the four quadrants, the radial symmetry is improved, and very few non-radially oriented fibers.
3D₁~ 3D_ThreeWith respect to the cellulosic fiber structure 20 in which very radially oriented fibers are distributed within the low basis weight area 26. 3D₁~ 3D_ThreeIn turn, an increasing trend to cellulosic fiber structures 20 with two basis weights is observed, whereas FIG.₁~ 3D_ThreeEach of the cellulosic fiber structures 20 represented by has a very low percentage of non-radially oriented fibers. 3D₁~ 3D_ThreeAlso shows good radial symmetry within the low basis weight area 26.
In general, for the purposes of the present invention, at least FIG.₁~ 3C₂As shown in FIG. 3D, preferably FIG.₁~ 3D_ThreeIt is considered that the cellulosic fiber structure having a radial orientation of the degree shown in the above is “essentially radially oriented” and meets the radial orientation criteria of the claims. Fig. 1, 2D_Three, 3C₂, And 3D_ThreeShows a cellulosic fibrous structure 20 that falls within the scope of the claimed invention (only these figures fall within the scope of claim 5).
Of course, not all of the low basis weight areas 26 within a particular cellulosic fibrous structure 20 meet the above criteria for radial orientation and low basis weight areas. Due to the usual anticipated changes in the manufacturing process, the low basis weight area 26 in the cellulosic fiber structure 20 is not considered to have the above two areas, or as described above. Some do not have a plurality of essentially radially oriented fibers, while others (adjacent) have low basis weight areas that meet both criteria. For the purposes of the present invention, the cellulosic fibrous structure 20 has a low basis weight area 26 that meets both of the above criteria, preferably at least 10%, more preferably at least 20%.
Since it is not practical to inspect each low basis weight area 26 within the specific cellulosic fiber structure 20, the percentage of low basis weight areas 26 that meet the criteria may be determined as follows.
Cellulosic fiber structure 20 is divided into three equal parts, preferably three three equal parts oriented in the machine direction (if known). A Cartesian coordinate system is applied to each of the three divided parts, and units corresponding to the machine direction of the low basis weight area 26 and the pitch in the direction across the machine are attached. Using a random number generator, 33 sets of coordinate points are selected for each outer three equal parts, and 34 sets of coordinate points are selected for the middle three equal parts, for a total of 100 coordinate points. Each coordinate point corresponds to the low basis weight area 26. If the coordinate point does not coincide with the low basis weight area 26 and corresponds to the high basis weight area 24, the low basis weight area 26 closest to the coordinate point is selected.
The 100 low basis weight areas 26 thus designated are analyzed as described above, optionally using a magnifying glass or an optical microscope. The percentage of low basis weight area 26 that meets both criteria determines the percentage for that particular cellulosic fibrous structure 20.
Of course, if a particular cellulosic fiber structure 20 does not have 100 low basis weight areas 26, or sampling that is representative of several individual cellulosic fiber structures 20 is desired, 100 points may be Divide into individual cellulosic fiber structures 20 and add up to determine the percentage of the sample.
Of course, individual cellulosic fiber structures 20 are randomly selected to maximize the chances of taking a truly representative sample. Individual cellulosic fiber structures 20 can be randomly selected by assigning a series of numbers to each cellulosic fiber structure 20 in a package or roll. The numbered cellulosic fiber structures 20 are randomly selected using another random number generator so that 1 to 10 cellulosic fiber structures 20 are obtained for analysis. Within 1-10 individual cellulosic fiber structures 20, 100 Cartesian points are divided as evenly as possible. The low basis weight areas 26 corresponding to these Cartesian points are then analyzed as described above.
apparatus
Many components of the equipment used to make the cellulosic fibrous structure 20 of the present invention are well known in the paper industry. As shown in FIG. 4, the apparatus includes means 44 for depositing a liquid carrier and cellulosic fibers contained therein onto a liquid-permeable, fiber-retaining molding element 42.
The liquid-permeable and fiber-retaining molding element 42 may be a molding belt 42, the center of the apparatus, and an apparatus away from the prior art for producing the cellulosic fiber structure 20 described and claimed herein. Represents one component. In particular, the liquid-permeable and fiber-retaining molding element comprises a protrusion 59 that forms the low basis weight area 26 of the cellulosic fiber structure 20 and an intermediate ring that forms the high basis weight area 24 of the cellulosic fiber structure 20. Part 65.
The apparatus further includes a secondary belt 46, after the bulk of the liquid carrier is discharged and the cellulosic fibers are retained on the forming belt 42, the fiber structure 20 moves onto the belt. The secondary belt 46 can further include a pattern of joints or protrusions that do not coincide with the areas 24 and 26 of the cellulosic fibrous structure 20. The forming and secondary belts 42 and 46 travel in the directions indicated by arrows A and B, respectively.
After the liquid carrier and the cellulosic fibers contained therein have been deposited on the forming belt 42, the fiber structure 20 is transferred to a known drying means 50a and 50b, such as a blow dryer 50a and / or a Yankee drying drum 50b. Dry by either or both. The apparatus may also include a doctor blade 68 for shortening or creping the fiber structure 20.
When the forming belt 42 is selected as a forming element of an apparatus used for manufacturing the cellulosic fiber structure 20, the forming belt 42 has two mutually facing surfaces, a first surface 53, as shown in FIG. And has a second surface 55. The first surface 53 is the surface of the forming belt 42 that contacts the fibers of the cellulosic structure 20 to be formed. The first surface 53 is referred to in this field as the side of the forming belt 42 that contacts the paper. The first surface 53 has two areas 53a and 53b that are geometrically different. Zones 53a and 53b are distinguished from the second opposing surface 55 of the forming belt 42 by the amount of change in the orthogonal direction. Such a change in the orthogonal direction is considered to be in the Z direction. As used herein, “Z direction” means the direction in which the forming belt 42 is considered to be a plane, that is, a two-dimensional structure, generally orthogonal to the XY plane of the forming belt 42 and away from that plane. To do.
The molded belt 42 must be able to withstand all of the known stresses and operating conditions in which the cellulosic two-dimensional structure is processed and manufactured. A particularly preferred forming belt 42 is a commonly assigned US Pat. No. 4,514,345, incorporated herein by reference for the purpose of illustrating a forming element particularly suitable for use in the present invention and a method for making such a forming element. According to the disclosure of Johnson et al. On April 30, 1985), it can be manufactured in particular according to FIG.
The forming belt 42 is liquid permeable in at least one direction, in particular from the first surface 53 of the belt, through the forming belt 42 and towards the second surface 53 of the forming belt 42. As used herein, “liquid permeable” means the conditions under which a fibrous carrier of fibrous slurry can permeate through the forming belt 42 without significant hindrance. Of course, it may be beneficial or even necessary to apply a slight differential pressure to help the liquid pass through the forming belt 42 in order to ensure that the forming belt 42 has adequate permeability.
However, it is not necessary for the entire surface of the forming belt 42 to be liquid permeable, which is rather undesirable. It is only necessary that the fibrous carrier of the fibrous slurry be easily removed from the slurry, leaving an undeveloped fiber structure 20 of deposited fibers on the first surface 53 of the forming belt.
The forming belt 42 is also fiber retaining. As used herein, when a part retains the majority of the fibers deposited thereon in a macroscopically predetermined pattern or geometry, regardless of the orientation or placement of a particular fiber Such parts are considered “fiber retention”. Of course, we do not expect the fiber-retaining parts to retain 100% of the fibers deposited on them (especially when the fiber liquid carrier is drained from such parts), and such retention is permanent. I do not expect that. It is only necessary that the fiber be held on the forming belt 42 or other fiber holding part for a time sufficient to complete each step of the process.
The forming belt 42 has a reinforcing structure 57 and a row of patterned protrusions 59 connected to the reinforcing structure 57 in a face-to-face relationship and defines two mutually facing faces 53 and 55. The reinforcing structure 57 may include a porous element such as a woven screen or other opening structure. The reinforcing structure 57 is substantially liquid permeable. A suitable porous reinforcing structure 57 is a screen having a mesh size of about 6 to about 30 filaments / cm. The openings between the filaments may be generally square, as shown, or may have other desired cross sections. Filaments can be formed from polyester strands, woven or non-woven fabrics. In particular, it has been found that a 48 × 52 mesh double layer reinforcing structure 57 is effective.
One surface 55 of the reinforcing structure 57 is substantially macroscopically flat and includes a surface 53 facing the outside of the forming belt. The face facing the inside of the forming belt 42 is often referred to as the back side of the forming belt 42 and, as described above, contacts at least a portion of the rest of the apparatus used for the papermaking operation. The surface 53 of the reinforcing structure 57 facing outwardly on the opposite side can be called the side in contact with the fibers of the forming belt 42 because the fibrous slurry is deposited on this surface 53 of the forming belt 42.
A patterned row of protrusions 59 is connected to the reinforcing structure 57 and preferably includes individual protrusions 59 extending outwardly from the inwardly facing surface 53 of the reinforcing structure 57 as shown in FIG. As the fiber slurry is deposited on the forming belt 42, the protrusions 59 are also considered to come into contact with the fibers because the patterned row of protrusions 59 receives the fiber slurry and may in fact be covered by the fiber slurry. .
The protrusions 59 are connected to the reinforcement structure 57 by known methods, but in a particularly preferred method, each protrusion 59 in the patterned row of protrusions 59 is not connected individually to the reinforcement structure 57, but cured. As a batch manufacturing method for blending a photosensitive polymer photosensitive resin, a plurality of protrusions 59 are connected to a reinforcing structure 57. The patterned row of protrusions 59 is generally continuous with a liquid material when the material is cured, forming part of the protrusion 59 and contacting it as shown in FIG. Preferably, the reinforcing structure 57 is formed by manipulating it so as to at least partially surround it.
As shown in FIG. 6, the plurality of conduits into which the fibers of the fiber slurry enter extend from the free end 53b of the protrusion 59 to the base 53a of the surface 53 facing the outside of the reinforcing structure 57 in the Z direction. Arrange the patterned rows of protrusions 59. This arrangement provides a limited geometric structure for the forming belt 42 and allows the liquid carrier and the fibers therein to flow into the reinforcing structure 57. The annular portion 65 between adjacent protrusions 59 forms a conduit with limited flow resistance depending on the pattern, size and spacing of the protrusions 59.
The protrusions 59 are separated and preferably regularly spaced so that no major weaknesses are formed in the substantially continuous network structure 24 of the cellulosic fiber structure 20. The liquid carrier can flow through the annular portion 65 between adjacent protrusions 59 to the reinforcing structure 57, on which the fibers can be deposited. More preferably, the substantially continuous network 24 of the cellulosic fibrous structure 20 (which is formed around and between the protrusions 59) ensures that the applied tensile load is more uniform across the fibrous structure 20. Thus, the protrusions 59 are distributed in a non-random repeating pattern. Most preferably, the protrusions 59 are symmetrically zigzag in a row so that adjacent low basis weight areas 26 in the resulting fiber structure 20 are not aligned with either major direction that may be subjected to tensile loading. .
Returning to FIG. 5, the protrusions 59 stand upright and connect at their base 53a to the face 53 facing the outside of the reinforcing structure 57, away from this face 53 and in the patterned row of protrusions 59, It extends from the surface 53 facing the outside of the reinforcing structure 57 to the end portion 53b, which is the farthest point in the perpendicular direction. Thus, the surface 53 facing the outside of the forming belt 42 is limited to two heights. The base portion of the surface 53 facing outward is limited by the surface of the reinforcing structure 57, and the base portion 53a of the protruding portion 59 is connected thereto, but of course, the protruding portion 59 surrounds the reinforcing structure 57 by solidification. Any material is considered. The height of the end of the outwardly facing surface 53 is limited by the end 53b of the patterned row of protrusions 59. The opposing inwardly facing surface 55 of the forming belt 42 is limited by another surface of the reinforcing structure 57, but of course any material of the protrusion 59 that surrounds the reinforcing structure 57 by solidification is considered. This surface is opposite to the direction in which the protrusion 59 extends.
The protrusion 59 extends from about 0.05 millimeters to about 1.3 millimeters (0.002 to 0.050 inches) outward from the base of the surface 53 facing the outside of the reinforcement structure 57 in a direction orthogonal to the surface of the forming belt 42. . Obviously, when the elongation of the protrusion 59 in the Z direction is zero, the basis weight of the cellulosic fiber structure 20 becomes almost constant. Thus, if it is desired to minimize the basis weight difference between adjacent high basis weight areas 24 and low basis weight areas 26 of cellulosic fibrous structure 20, generally shorter protrusions 59 should be used.
As shown in FIG. 6, the protrusion 59 preferably does not have a sharp corner particularly in the XY plane so that stress does not concentrate in the low basis weight area 26 of the cellulosic fiber structure 20 of FIG. A particularly preferred protrusion 59 has a curved rhombohedral shape with a diamond-shaped cross-section with rounded corners.
Regardless of the cross-sectional area of the protrusion 59, the side surfaces of the protrusion 59 are generally parallel to each other and can be orthogonal to the surface of the forming belt. Alternatively, the projecting portion 59 is tapered to some extent, and can have a right circular truncated cone shape as shown in FIG.
The protrusion 59 does not have to have a uniform height, or the end 53b of the protrusion 59 need not be equidistant from the base 53a of the surface 53 facing the outside of the reinforcing structure 57. If it is desirable to incorporate a more complex pattern into the fiber structure 20 than the pattern shown in the figure, this will be limited by the geometry of some of the upstanding protrusions 59 limited by the height in the Z direction. This is achieved by providing a basis weight that is different from the basis weight obtained in the area of the fiber structure 20 that has a geometric structure and each height is defined by protrusions 59 of other heights. Alternatively, three or more are connected by other methods, for example, by connecting the protrusion 59 having a uniform size to the reinforcing structure 57 having a flatness that varies significantly with respect to the extension of the protrusion 59 in the Z direction. This is achieved by a forming belt 42 having an outwardly facing surface 53, which is limited by the height of the surface.
As shown in FIG. 6, the patterned row of protrusions 59 preferably represents the projected surface area of the molded belt 42 as a percentage, without considering the ratio of the reinforcing structure 57 to the projected surface area of the molded belt 42. Thus, the minimum surface area ranges from about 20% of the total protruding surface area of the forming belt 42 to about 80% total of the total protruding surface area of the forming belt 42. The ratio of the patterned row of protrusions 59 to the total surface area protruding of the forming belt 42 is the respective protrusion as seen at the largest protrusion in the orthogonal direction with respect to the surface 53 facing the outside of the reinforcing structure 57. Think of it as the sum of the protruding areas of part 59.
As the ratio of the protrusions 59 to the total surface area of the forming belt 42 decreases, the above-described high basis weight substantially continuous network structure 24 of the fiber structure 20 increases, and the economics of using raw materials decreases. Furthermore, as the fiber length increases, the distance between the adjacent protrusions 59 and the opposing sides of the adjacent protrusions 59 of the forming belt 42 should increase. Otherwise, the fibers bridge the adjacent protrusions 59, pass through the conduits between the adjacent protrusions 59, and cannot penetrate the reinforcing structure 57 limited by the surface area of the base 53a.
The second surface 55 of the forming belt 42 may have a limited significant geometric structure, or may be a substantially macroscopic single plane. As used herein, “substantially macroscopically single plane” means that the geometric structure of the forming belt 42 is a two-dimensional structure and is slightly acceptable from absolute flatness. It has only a deviation, which means that it does not adversely affect the performance of the forming belt 42 in the production of the cellulosic fiber structure 20 described above and below. As long as the geometric structure of the first surface 53 of the forming belt 42 is not interrupted by the greater displacement and the forming belt 42 can be used in the manufacturing process described herein, the structure of the second surface 55 is geometric. Or a substantially single plane. The second surface 55 of the forming belt 42 can contact equipment used in the manufacturing process of the cellulosic fiber structure 20 and is referred to in this field as the machine side of the forming belt 42.
The protrusion 59 defines a plurality of annular portions 65 having different flow resistances on the liquid permeable portion of the forming belt 42. One way to provide different areas is shown in FIG. The protrusions 59 of the forming belt of FIG. 6 are arranged at substantially equal intervals from the adjacent protrusions 59 to form a substantially continuous network-shaped annular portion 65 between the adjacent protrusions 59.
An opening 63 extends in the Z direction through substantially the center of each of the plurality of protrusions 59 or through each protrusion 59, and this opening allows the end 53 b of the protrusion 59 to be connected to the outside of the reinforcing structure 57. The liquid is in communication between the base 53a of the surface 53 facing the surface. Unlike the flow resistance of the annular portion 65 between the adjacent protrusions 59, the flow resistance of the opening 63 passing through the protrusion 59 is generally larger than that. Accordingly, more liquid carrier is discharged through the annular portion 65 between the adjacent protrusions 59 than the liquid carrier that passes through the opening 63 surrounded by the free end 53 b of the specific protrusion 59. Since more liquid carrier passes through the annular portion 65 between the adjacent protrusions 59 than the liquid carrier that passes through the opening 63, more fibers than the fibers deposited on the reinforcing structure 57 immediately below the opening 63 are adjacent. It accumulates on the reinforcing structure 57 immediately below the annular portion 65 between the protrusions 59.
Annular portion 65 and opening 63 define high and low flow areas in forming belt 42, respectively. The initial material flow rate of the liquid carrier through the annular portion 65 is greater than the initial material flow rate through the opening 63.
Of course, since the protrusion 59 is impermeable to the liquid carrier, the liquid carrier will not flow through the protrusion 59. However, depending on the height of the end 53b of the protrusion 59 and the length of the cellulosic fiber, the cellulosic fiber may be deposited on the end 53b of the protrusion 59.
As used herein, “initial material flow rate” means the flow rate of the liquid carrier when the liquid carrier is first introduced into the forming belt 42 and deposited thereon. Of course, in both flow zones, the openings 63 or annular portions 65 that limit these zones are dispersed in the liquid carrier and blocked by cellulosic fibers held by the forming belt 42, so that the material flow rate over time is increased. descend. Due to the difference in flow resistance between the opening 63 and the annular portion 65, a means of holding different basis weight cellulosic fibers in different patterns in different areas of the forming belt 42 is obtained.
This difference in flow rate through each zone is referred to as “step evacuation” in the sense that there is a step discontinuity between the initial flow rates of the liquid carrier through the high and low flow zones. As described above, gradual ejection can be effectively used to deposit different amounts of fibers in different areas 24 and tufted patterns in cellulosic fiber structures 20.
More particularly, the high basis weight area 24 is a non-random repeat that substantially corresponds to the high flow area of the forming belt 42 (annular portion 65) and the high flow stage of the process used to produce the cellulosic fiber structure 20. It occurs in a pattern. The low basis weight area 26 is a non-random repetition that substantially corresponds to the low flow area of the forming belt 42 (openings 63 and protrusions 59) and the low flow stage of the process used to produce the cellulosic fiber structure 20. It occurs in a pattern.
The flow resistance of the entire forming belt 42 can be easily measured by techniques well known to those skilled in the art. However, it is more difficult to measure the flow resistance in the high and low flow areas and the difference in flow resistance between them due to the small size of the high and low flow areas. However, flow resistance can be inferred from the hydraulic radius of the area in question. In general, the flow resistance is inversely proportional to the hydraulic radius.
The hydraulic radius of an area is defined as the area of the area divided by the wet perimeter of the area. The denominator often contains a constant such as 4. However, for this purpose, it is only important to examine the difference in the hydraulic radius of the zone, and constants may be included or omitted as desired. This is algebraically

Where the flow area is the area through the opening 63 of the protrusion 59, or the flow area between adjacent protrusions 59, as defined in more detail below, and the wet perimeter. The length is the linear dimension around the area in contact with the liquid carrier. Some common shaped hydraulic radii are well known, show some common shaped hydraulic radii, and disclose how to find irregular shaped hydraulic radii It is described in many documents such as Mark's Standard Handbook for Mechanical Engineers, 8th edition, which is included here as a reference.
The hydraulic radius of a particular forming element 42 or part thereof can be calculated by considering the smallest repeating unit that defines a unit cell, i.e. a complete protrusion 59 and an annular portion 65 surrounding the protrusion 59. Of course, the unit cell should measure the hydraulic radius at the height of the protrusion 59 and the annular portion 65 which gives the greatest restriction to the flow. For example, the height of the photosensitive resin protrusion 59 from the reinforcing structure 57 may affect the flow resistance. If the protrusion 59 is tapered, the calculated water pressure radius can be corrected by taking into account the air permeability of the forming element 42, as will be described with respect to Table I below.
Without such correction, the apparent ratio of hydraulic radii, discussed below, would be smaller than the hydraulic radius actually present on the forming element 42. The hydraulic radius ratios described in the examples below are not corrected, but are fully useful for such examples.
With reference to FIG. 6, possible unit cells for the forming element 42 are indicated by broken lines CC. Of course, boundaries formed from unit cells but not constituting the wet perimeter of the channel are not taken into account in the calculation of the hydraulic radius.
The flow area used for the calculation of the hydraulic radius does not take into account the limitations imposed by the reinforcing structure 57 directly below the protrusion 59. Of course, as the size of the opening 63 decreases, a smaller pattern is selected, or because the diameter of the opening 63 is smaller, it does not have the radial orientation required in the low basis weight area 26, or A cellulosic fibrous structure 20 may be formed having three zones distinguished by basis weight. Such a change may be due to the flow resistance imposed by the reinforcing structure 20.
For the forming belt shown in FIG. 6, two important areas are defined as follows. The selected area includes an annular periphery that surrounds the protrusion 59. The elongation in the XY direction of the ring-shaped peripheral portion with respect to the specific protrusion 59 is half of the radial distance from the protrusion 59 to the adjacent protrusion 59. Thus, the area 69 between adjacent protrusions 59 has a boundary in the middle thereof, which boundary is an annular perimeter that defines such an annular portion 65 between adjacent protrusions 59 of adjacent protrusions 59. Is in contact with the department.
In addition, since the protrusion 59 extends in the Z direction to a certain height above the rest of the reinforcing structure 57, little fiber is deposited in the area above the protrusion 59. This is because the fibers deposited in the portion of the reinforcing structure 57 corresponding to the annular portion 65 between the opening 63 and the adjacent protrusion must first accumulate to the height of the free end 53b of the protrusion 59, This is because the additional fibers are not discharged into the opening 63 or the annular portion 65 between the adjacent protrusions 59 and remain in the uppermost portion of the protrusion 59 after that.
One non-limiting example of a forming belt 42 that has been found to work effectively with the present invention has a 52 double mesh woven reinforcement structure 57. The reinforcing structure 57 is made of fibers having a warp diameter of about 0.15 millimeters (0.006 inches) and a shute diameter of about 0.18 millimeters (0.007 inches) and has an open area of about 45-50%. This reinforcing structure 57 can pass a flow of air of about 36,300 standard liters per minute (1,280 standard cubic feet per minute) with a differential pressure of about 12.7 millimeters (0.5 inches) of water. The thickness of the reinforcing structure 57 is approximately 0.76 millimeters (0.03 inches), taking into account the joint formed by the weave pattern between the two faces 53 and 55 of the molded belt 42.
A plurality of symmetrically zigzag protruding portions 59 are connected to the reinforcing structure 57 of the forming belt 42. Each protrusion 59 is spaced from an adjacent protrusion with a machine direction pitch of about 24 millimeters (0.096 inches) and a machine cross direction pitch of about 1.3 millimeters (0.052 inches). The protrusions 59 are provided at a density of approximately 47 protrusions 59 per square centimeter (approximately 200 protrusions 59 per square inch).
Each protrusion 59 has a width between opposing corners in the cross machine direction of about 0.9 millimeters (0.036 inches) and a length between opposing corners in the machine direction of about 1.4 millimeters (0.054 inches). The protrusion 59 extends about 0.1 millimeter (0.004 inch) in the Z direction from the base 53a of the surface 53 facing the outside of the reinforcing structure 57 to the free end 53b of the protrusion 59.
Each protrusion 59 is disposed in the center and has an opening 63 extending from the free end 53b of the protrusion to the base 53a of the protrusion 59, so that the free end 53b of the protrusion is in fluid communication with the reinforcement structure 57. Yes. Each opening 63 located in the center of the protrusion 59 is generally oval with a major axis of about 0.8 millimeters (0.030 inches) and a minor axis of about 0.5 millimeters (0.021 inches). With the protrusion 59 connected to the reinforcing structure 57, the air permeability of the formed belt 42 is about 17,300 standard liters per minute (610 standard cubic feet per minute) with a differential pressure of about 12.7 millimeters (0.5 inches) of water. The protrusion 59 extends about 0.1 mm above the surface 53a of the reinforcing structure 57. With this forming belt 42, the fiber structure 20 shown in FIG. 1 is manufactured.
As shown in FIG. 4, the apparatus further includes the liquid carrier and the cellulosic fibers contained therein on the forming belt 42, and more particularly on the face 53 having discontinuous upstanding protrusions 59 of the forming belt 42. , Means 44 for depositing the reinforcing structure 57 and the protrusion 59 so that they are completely covered by the fibrous slurry. As is well known in the art, the head box 44 can be used for this purpose. Several types of headboxes 44 are known in the field, but headboxes 44 found to be effective generally apply a continuous slurry of fibrous slurry onto the surface 53 facing the outside of the forming belt 42. And a conventional two-wire headbox 44 to be deposited.
The means 44 for depositing the fibrous slurry and the forming belt 42 are relatively moved so that generally a certain amount of the liquid carrier and the cellulosic fibers contained can be deposited on the forming belt 42 in a continuous process. Alternatively, the liquid carrier and contained cellulosic fibers can be deposited on the forming belt 42 in a batch process. As the differential velocity between the forming belt 42 and the depositing means 44 increases or decreases, more or less liquid carrier and contained cellulosic fibers can be deposited on the forming belt 42 per unit time, respectively. Furthermore, it is preferable that the means 44 for depositing the fibrous slurry on the permeable forming belt 42 can be adjusted.
Also provided are means 50a and / or 50b for drying the fibrous slurry from the undeveloped cellulosic fiber structure 20 of fibers to form a two-dimensional cellulosic fiber structure 20 having a consistency of at least about 90%. You can also Any convenient drying means 50a and / or 50b well known in the paper industry can be used to dry the undeveloped cellulosic fiber structure 20 of the fibrous slurry. For example, press felts, thermal hoods, infrared radiation, blower dryers 50a, and Yankee dryer drums 50b, each used alone or in combination, are effective and well known in the art. In a particularly preferred drying method, the blower dryer 50a and the Yankee drying drum 50b are sequentially used.
If desired, the apparatus of the present invention can further include an emulsion roll 66 as shown in FIG. The emulsion roll 66 distributes an effective amount of chemicals to the forming belt 42 or, if desired, the secondary belt 46 during the above steps. This chemical acts as a release agent to prevent unwanted adhesion of the cellulosic fiber structure 20 to the forming belt 42 or the secondary belt 46. Furthermore, the emulsion roll 66 can also be used to apply and treat chemicals on the forming belt 42 or the secondary belt 46, thereby extending its useful life. Preferably, the emulsion is applied to the geometric structure surface 53 facing away from the forming belt 42 when the forming belt 42 is not in contact with the fiber structure 20. This is typically done when the cellulosic fiber structure 20 moves from the forming belt 42 and the forming belt 42 is on the return path.
Suitable chemicals for the emulsion include water, a high-speed turbine oil known as Regal Oil sold under the product number R & O 68 Code 702 from Texas, Texas Texas Oil Company, Shex Chemical Company, Rolling Meadows, Illinois, Dimethyldistearylammonium chloride sold by Inc. as AOGEN TA100, cetyl alcohol from Procter & Gamble Company from Cincinnati, Ohio, and an antioxidant such as Cyanox 1790 from American Cyanamid from Wayne, New Jersey There is a composition comprising Also, if desired, a cleaning shower or spray (not shown) can be used to clean the fibers and other residues remaining after the cellulosic fiber structure 20 moves from the forming belt 42 from the forming belt 42. You can also
Although desired for the production of the cellulosic fiber structure 20 of the present invention, a highly preferred step is to shorten the fiber structure 20 after it has dried. As used herein, “shortening” is to shorten the length of the fiber structure 20 by rearranging the fibers and separating the bonds between the fibers. The shortening can be done by several well-known methods, but the most common and preferred method is creping.
The creping process can be performed in association with the drying process by using the Yankee drying drum 50b. In the creping process, the cellulosic fiber structure 20 is preferably attached to the surface of the Yankee drying drum 50b, and then from that surface, the doctor blade 68 is used, and the relative relationship between the doctor blade 68 and the surface on which the fiber structure 20 is attached is Eliminate by physical exercise. The doctor blade 68 is oriented with a component that is orthogonal to the direction of relative motion between the surface and the doctor blade 68, and is preferably substantially orthogonal thereto.
Also, means for applying a differential pressure to selected portions of the fiber structure 20 can be provided. The differential pressure can cause the areas 24 and 26 of the cellulosic fibrous structure 20 to be densified or de-densified. The differential pressure may be applied to the cellulosic fiber structure 20 at any step before the liquid carrier is discharged excessively, but preferably while the cellulosic fiber structure 20 is an undeveloped cellulosic fiber structure 20. Make it work. If the excess liquid carrier is drained before the differential pressure is applied, the fibers become too stiff and do not fit well with the patterned row geometry of the protrusion 59, resulting in a difference in density as described above. A cellulosic fibrous structure 20 is formed that does not have any areas.
If desired, the sections 24 and 26 of the cellulosic fibrous structure 20 can be further divided by density. In particular, a specific high basis weight area 24 or a specific low basis weight area 26 can be densified or de-densified. This can be achieved by moving the cellulosic fiber structure 20 from the forming belt 42 to a secondary belt 46 having protrusions that do not coincide with the separated protrusions 59 of the forming belt 42. During or after movement, the protrusions of the secondary belt 46 compress certain areas of the areas 24 and 26 of the cellulosic fibrous structure 20 and densify such areas. Of course, the degree of densification of the high basis weight area 24 is greater than that of the low basis weight area 26.
When the selected portion is compressed by the protruding portion of the secondary belt 46, such a portion is densified and the bond between the fibers becomes strong. Such bonding increases the tensile strength at such locations and increases the overall tensile strength of the cellulosic fiber structure 20. Preferably, the densification is performed before the excess liquid carrier is drained, the fibers become too stiff and do not fully fit the patterned row geometry of the protrusions 59.
Alternatively, selected locations of the various areas 24 and 26 can be de-densified to increase the thickness and absorbency of such locations. De-densification involves moving the cellulosic fiber structure 20 from the formed belt 42 to a secondary belt 46 having vacuum permeable areas that do not coincide with the protrusions 59 or the areas 24 and 26 of the cellulosic fiber structure 20. Can be done. After moving the cellulosic fiber structure 20 to the secondary belt 46, a positive pressure or a fluid differential pressure below atmospheric pressure is applied to the vacuum permeable area of the secondary belt 46. This fluid differential pressure causes the fiber at the location corresponding to the vacuum permeable area to be biased in a plane perpendicular to the secondary belt 46. When the fibers exposed to the fluid differential pressure are biased, the fibers move away from the surface of the cellulosic fiber structure 20, and the thickness increases.
Manufacturing method
The cellulosic fiber structure 20 of the present invention can be produced by a production method including the following steps. In the first step, a plurality of cellulosic fibers are placed in a liquid carrier. Cellulosic fibers are not dissolved in the liquid carrier, but are simply dispersed therein. In addition, a liquid-permeable and maintenance-holding molding element 42 such as a molding belt 42 is prepared. The forming element 42 has liquid permeable areas 63 and 65 and upstanding protrusions 59. Also used is a means 44 for depositing the liquid carrier and the cellulosic fibers contained on the forming element 42.
The forming belt 42 has high and low flow liquid permeable areas defined by an annular portion 65 and an opening 63, respectively. The forming belt 42 also has an upstanding protrusion 59.
The liquid carrier and contained cellulosic fibers are deposited on a forming belt 42 shown in FIG. The liquid carrier is discharged through the forming belt 42 in two simultaneous stages, a high flow stage and a low flow stage. In the high flow stage, the liquid carrier passes through a liquid permeable high flow area at a specific initial flow rate and is discharged until clogging occurs (or liquid carrier is no longer introduced into this part of the forming belt 42). In the low flow stage, the liquid carrier is discharged through the low flow area of the forming element 42 at a specific initial flow that is lower than the initial flow through the high flow area.
Of course, the flow through both the high and low flow areas in the forming belt 42 will decrease over time due to the expected blockage of both areas. Although there is no theoretical support, the low flow area may be occluded before the high flow area is occluded.
Although there is no theoretical support, the first blockage of the area that occurs is based on factors such as flow area, wet perimeter, shape and distribution of the low flow area, and the hydraulic radius of such areas is small. This can occur because of the high flow resistance, or because of the high flow rate through such areas and high fiber deposition. The low flow area can include, for example, an opening 63 through the protrusion 59, which has a greater flow resistance than the liquid permeable annular portion 65 between adjacent protrusions 59.
In both stages of discharge, certain cellulosic fibers are simultaneously affected by orientation by the high and low flow areas. These effects cause the fibers to be oriented radially and bridge across the surface of the protrusion 59 having infinite flow resistance. This radial cross-linking causes the high basis weight area 24 to spread across each discontinuous low basis weight area 26. The low flow area does not cause excessive accumulation of fibers at the center of the low flow area, but has an orientational effect such that such cross-linking occurs, minimizing the occurrence of an intermediate basis weight area 25, or Stop.
It is important that the ratio of flow resistance between the opening 63 and the annular portion 65 is properly matched. If the flow resistance through the opening 63 is too small, the intermediate basis weight area 25 may be formed generally in the center of the low basis weight area 24. This arrangement results in a cellulosic fiber structure 20 having three types of zones. Conversely, too much flow resistance can result in low basis weight areas with irregular or other non-radial fiber distributions.
The flow resistance of the opening 63 and the annular portion 65 can be determined using the hydraulic radius as described above. According to the examples analyzed below, the ratio of the hydraulic radius of the annular portion 65 to the opening 63 is about 5 to about 31 protrusions 59 per square centimeter (30 to 200 protrusions 59 per square inch). It should be at least about 2 for the forming element 42 it has. Lower hydraulic radii, such as at least about 1.1, have over 59 protrusions 59 per square centimeter (200 per square inch) and up to about 78 protrusions per square centimeter (500 per square inch) It is considered suitable for the element 42.
Table I shows the geometric structure of the five forming elements 42 used to produce the example cellulosic fiber structure 20 analyzed in more detail below. With respect to the first column of Table I, the area of the annular portion 65, expressed as a percentage of the total surface area of the forming element 42, is 30% or 50%. As shown in the second column, the surface area of the opening 63, expressed as a percentage of the total surface area of the molding element 42, is 10-20%. The third column shows the degree of the protrusion 59 on the reinforcing structure 57. In the fourth column, the theoretical ratio of the hydraulic radius to the opening 63 of the annular portion 65 is calculated. In the fifth column, the actual ratio of the hydraulic radius is calculated as explained below.
The actual water pressure radius and its ratio were repeatedly calculated from the air permeability of the forming element 42 with and without the protrusion 59. The theoretical size of the protrusion 59, and thus the hydraulic radius, can be easily found from the drawings used to build the molding element 42, but the actual size varies to some extent due to variations inherent in the manufacturing process. To do.
The actual size of the protrusion 59, and thus the annular portion 65 and the opening 63, is such that the air permeability of the reinforcing structure 57 without the protrusion 59 and the air permeability of the reinforcing structure 57 with the protrusion 59 It was approximated by comparing with sex. The actual air permeability was easily measured using known techniques and was smaller than the value obtained by theoretically subtracting the protrusion 59 from the flow area through the reinforcing structure 57.
By knowing the actual and theoretical air permeability differences of the forming element 42 with the protrusion 59 in place, the wall of the protrusion 59 tapers equally toward the annular portion 65 and the opening 63. Assuming that-is attached, the size of the protrusion 59 necessary to obtain such an actual air flow can be obtained in an iterative fashion, using normal numbers.

The forming elements 42 each had 31 protrusions 59 per square centimeter (200 protrusions 59 per square inch). Of course, only the ratio of the unit cell to the wet area of the flow area is considered, and the ratio is constant regardless of whether the size of the unit cell is enlarged or reduced. It is unrelated to the size of 65.
A hydraulic radius of 0.52 to 1.27 is used for the forming element 42 used to construct the cellulosic fiber structures 20 of the various examples shown in Table II below. For the construction of the cellulosic fiber structure 20 of each Example shown in Table III below, a molding element 42 having a hydraulic radius ratio of 2.05 is used.
From these examples, a forming element 42 having a hydraulic radius ratio of at least about 2 is considered effective. Of course, since the material flow ratio is proportional to at least the square of the hydraulic radius ratio, depending on the Reynolds number, a material flow ratio of at least 2, and possibly greater than 4, is expected to be effective.
As expected, the forming element 42 of the present invention can use a hydraulic radius ratio as low as 1.25 (although other factors can be adjusted to compensate for such a low ratio). For example, the absolute speed of the forming element 42 could be increased, or the relative speed between the forming element 42 and the liquid carrier could be matched near 1.0 speed ratio. It would also be effective to use short fibers such as Brazilian eucalyptus in the production of the cellulosic fiber structure 20 of the present invention.
For example, the preferred cellulosic fiber structure 20 of the present invention is manufactured using a forming element 42 having a hydraulic radius ratio of 1.50. The absolute speed of the forming element 42 was about 262 meters / minute (800 feet / minute) and the speed ratio between the liquid carrier and the forming element 42 was about 1.2. The forming element 42 had 31 protrusions 59 per square centimeter (200 protrusions 59 per square inch). The protrusion 59 occupies about 50% of the total surface area of the molding element 42, and the opening 63 therethrough occupies about 15% of the surface area of the molding element 42. The resulting cellulosic fiber structure 20 consists of about 60% northern softwood graft and about 40% chemical-thermo-mechanical softwood pulp (CTMP), both of which have a fiber length of about 2.5 to about 3.0 millimeters. there were. The resulting cellulosic fiber structure 20 had a low basis weight area 26 of approximately 25% and was within both of the above criteria.
Example
Using the different parameters shown in Table II, several non-limiting cellulosic fiber structures 20 were made. All samples are S-wrap two wire forming machines, 35.6 x 35.6 centimeters (14 x 14 inches) superimposed on a regular 84M 4 shed satin weaving wire that is fed through the nip and dried as usual Produced using a square sample forming element 42. All of these cellulosic fiber structures 20 use a forming element 42 having a speed of about 244 meters per minute (800 feet per minute) and form a liquid carrier at a rate approximately 20% higher than the speed of the forming element 42. Manufactured by supplying onto element 42. The resulting cellulosic fiber structures 20 each had a basis weight of about 19.5 grams / square meter (12 pounds / 3000 square feet).
The second column shows that the example in Table II shows 5 protrusions 59 per square centimeter (30 protrusions 59 per square inch) or 31 protrusions 59 per square centimeter (200 per square inch). It is shown that the projection 59 is constructed using the projection 59 having the size of the projection 59. The third column indicates that the percentage of the open area in the annular portion 65 between adjacent protrusions 59 is 10 or 20%. The fourth column represents the size of the cross-sectional area of the opening 63 as a percentage of the cross-sectional area of the protrusion 59. The fifth column indicates that the extent of the distal end 53b of the protrusion 59 on the reinforcement structure 57 is from about 0.05 millimeter (0.002 inch) to about 0.2 millimeter (0.008 inch). The sixth column indicates that the fiber type is a northern softwood graft with a fiber length of about 2.5 millimeters or a Brazilian eucalyptus with a fiber length of about 1 millimeter.
All of the resulting cellulosic fiber structures 20 were examined without being expanded and expanded to 50x and 100x. The sample is qualitatively divided into two criteria: 1) the presence of two zones 24 and 26, three zones 24, 26 and a medium basis weight zone 25 generally in the center of the low basis weight zone 26, and 2) The radial orientation of the fiber was judged. Radial orientation was determined by the symmetry of the fiber distribution and the presence of non-radially (tangential or circumferential) oriented fibers.
The last column shows the classification of the cellulosic fiber structure 20 obtained. Each cellulosic fiber structure 20 of the examples shown in Table II was subjectively classified as follows using the above criteria.

Of course, depending on which criteria are applied, one embodiment of the cellulosic fiber structure 20 may fall into more than one category. If only one criterion is listed, the other criterion was determined to meet the conditions of the cellulosic fiber structure 20 of the present invention.

With respect to Table III, an example cellulosic fiber structure 20 was further produced by air drying on the same two wire forming machine using a full size forming wire. The forming element 42 had about 31 protrusions 59 per square centimeter (200 protrusions 59 per square inch), each extending about 0.1 millimeter (0.004 inch) on the reinforcing structure 57. . The protrusion 59 occupies about 50% of the surface area of the molding element 42, and the opening 63 occupies about 10% of the surface area of the molding element 42.
As shown in the second column, the ratio of the liquid carrier speed to the speed of the forming element 42 was 1.0 or 1.4. As shown in the third column, the liquid carrier was impinged on a roll supporting the forming element 42 at about 0% or 20% of its surface area. As shown in the fourth column, the resulting cellulosic fibrous structure 20 had a basis weight of about 19.5 or about 25.4 grams per square meter (12.0 or 15.6 pounds per 3,000 square feet). The same fibers as described above with respect to Table II were used as indicated in the fifth column. As shown in the sixth column, the forming element 42 had a speed of 230 or 295 meters / minute (700 or 900 feet / minute). As shown in the last column, the same criteria were applied to the classification of the cellulosic fiber structure 20 obtained.

As can be seen from Table III, in general, the ratio of liquid carrier speed to forming element 42 speed was the most important factor in classifying these resulting cellulosic fiber structures 20. In general, a speed ratio of 1.0 was effective for eucalyptus fibers, and a speed ratio of 1.4 was generally effective for northern softwood graft fibers. The speed of the forming element 42 was a slightly less important factor in the classification of the cellulosic fiber structure 20 obtained. In general, as the speed of the forming element 42 decreased, the tendency for irregular fiber distribution within the low basis weight area 26 also decreased.
Furthermore, it is clear that the resulting cellulosic fiber structure 20 is significantly affected by the type of fiber used. In general, the cellulosic fiber structure 20 with eucalyptus fibers is more sensitive to the speed of the liquid carrier to the forming element 42 and has a good two-zone cellulosic fiber structure with radially oriented fibers in the low basis weight zone 26. 20 or an undesirable three-zone cellulosic fiber structure 20 was obtained. When northern softwood graft fibers were used, a cellulosic fiber structure 20 having a boundary three zone or boundary irregular fiber distribution within a low basis weight zone 26 was produced.
Deformation
Instead of the cellulosic fiber structure 20 formed on the forming element 42 having the protrusions 59 through which the openings 63 pass, the fibers are radial on the forming element 42 as shown in FIGS. 7A and 7B. A cellulosic fiber structure 20 having a low basis weight area 26 oriented in the direction can be produced. In this molding element 42, the protrusions 59 ′ are radially divided, and the annular portion 65 ″ is limited to the radially oriented portion 59 ″.
As shown in FIG. 7A, radial portions 59 "can be connected at or near the center to prevent the formation of an intermediate basis weight area 25. With this arrangement, the cellulosic fibers have a radial portion 59". Can flow through the annular portion 65 "and bridge to the center of the radial portion 59".
Alternatively, as shown in FIG. 7B, the radial portion 59 "can be separated by a central opening 63 'so that it flows without resistance towards the center of the low flow area. Thus, it is not necessary to bridge the center of the radial portion 59 "of the protrusion 59 ', but instead the advantage of facilitating the radial flow without obstruction is obtained.
In the embodiment shown in FIGS. 7A and 7B, the radial portion 59 "can include a circular sector. Alternatively, the radial portion 59" is not generally circular and converges as it approaches the center of the low flow area. You can also.
It will be apparent to those skilled in the art that many other variations and combinations are possible within the scope of the claimed invention. All such variations and combinations are within the scope of the claims.

Claims (5)

A single thin layer cellulosic fibrous structure consisting essentially of two types of areas arranged in a repeating pattern, wherein the cellulosic fibrous structure comprises:
It has a relatively high basis weight and a first section, and a relatively low basis weight comprising substantially continuous network structure, and become surrounded by the first zone, a plurality of mutually A discontinuous second zone, the second zone comprising a plurality of essentially radially oriented fibers from the center ,
A cellulosic fibrous structure characterized in that the first area having a relatively high basis weight comprises a high basis weight area having different densities. A second area comprising low basis weight and a plurality of essentially radially oriented fibers in the plurality of second areas at least about 10% of the total number of the second areas in the cellulosic fibrous structure; The single thin layer cellulosic fibrous structure of claim 1 comprising. A second area comprising low basis weight and a plurality of essentially radially oriented fibers in the plurality of second areas at least about 20% of the total number of the second areas in the cellulosic fibrous structure; The single thin layer cellulosic fibrous structure of claim 1 comprising. The cellulosic fiber structure according to any one of claims 1 to 3, wherein the basis weight of the high basis weight area is at least 25% greater than the basis weight of the low basis weight area. From only two zones arranged in a repetitive pattern a single thin layer cellulosic fibrous structure consisting essentially of,
A first zone of relatively high basis weight and substantially continuous, load bearing network structure ; and
A plurality of mutually discontinuous zones surrounded by the first zone, the second zone having a lower basis weight than the first zone, wherein the fibers of the second zone are the second zone. characterized in that the eccentric part in the region formed by radially oriented in said first zone, cellulosic fiber structure.

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